The point is to give a very general map so people can see the over all layout of the server and where the landmarks are without giving you all the information. Try exploring about and you will get a good idea of what you are looking at fairly quickly.

The color indicates something about the overall biome of the map in that area, but it's not 'forest' and 'not forest'. If I recall correctly from when the map was made, the server has areas that predominate with maple forest, grass, spruce forest, and maybe something else. I don't remember which color indicates which biome though. Since the biomes are really well mixed, you won't be able to use those color changes to help you navigate or know where you are very well. It's just a general predominance. The lakes and mountaintops are accurate though.

ignore the shadings altogether, they're useless for navigation purposes. Mountains, water and landmarks are all you really need to take from that map - those are accurate. The rest is irrelevant space filler.